The present invention relates to a picture signal processing circuit which performs an image interpolation process for outputting pictures.
A conventional picture signal processing circuit wherein picture signal data compliant with analog video standards is used to carry out a digital format conversion compliant with digital standards for producing digital output is described in, for example, Japanese Unexamined Patent Publication No. 2002-369191. The structure of this picture signal processing circuit is shown in FIG. 6.
The picture signal processing circuit shown in FIG. 6 includes a video buffer memory 102, a video buffer memory control section 103, and a picture signal processing section 101 which includes an analog signal processing circuit 104 and a digital signal processing circuit 105. The video buffer memory 102 stores image data which has been decoded and converted to analog progressive data. The video buffer memory control section 103 performs output control of the data stored in the video buffer memory 102 based on the output format and an analog data effective line signal. The analog signal processing circuit 104 converts picture signal data compliant with the analog video standards, which is input from the video buffer memory 102, to an analog format, thereby performing signal processing for an analog output. The digital signal processing circuit 105 converts picture signal data compliant with the analog video standards, which is input from the video buffer memory 102, to a digital format, thereby performing signal processing for a digital output. Such a circuit which is capable of both analogly and digitally outputting picture signal data is disclosed in the above-mentioned publication, for example.
However, in the above-described conventional structure, picture signal data compliant with the progressive analog video standards is subjected to a digital format conversion to produce a digital output. Thus, video data cannot be output unceasingly during a picture display period that is defined in the progressive digital video standards. As a result, there is no picture signal data even in the video signal display period, and black data is output instead. This is caused by a difference in the image display period (active period) between the analog video standard shown in FIG. 7 (see Rec.ITU-R BT1358 “STUDIO PARAMETERS OF 625 AND 525 LINE PROGRESSIVE SCAN TELEVISION SYSTEMS”) and the digital video standard shown in FIG. 8 (see Rec.ITU-R BT1362 “INTERFACES FOR DIGITAL COMPONENT VIDEO SIGNALS IN 525- AND 625-LINE PROGRESSIVE SCAN TELEVISION SYSTEMS”).
Among the analog video standards, in the NTSC progressive standard (analog 525P standard) shown in FIG. 7, all of the fields are normalized with the 43rd to 525th lines during the video signal display period. On the other hand, in the NTSC progressive standard of the digital video standards (digital 525P standard) shown in FIG. 7, the odd-numbered fields are normalized with the 39th line to the 1st line of the next field, and the even-numbered fields are normalized with the 40th to 525th lines. In the PAL progressive standard of the analog video standards (analog 625P standard), all of the fields are normalized with the 45th to 620th lines during the video signal display period as shown in FIG. 8. On the other hand, in the PAL progressive standard of the digital video standards (digital 625P standard), the odd-numbered fields are normalized with the 45th to 620th line, and the even-numbered fields are normalized with the 46th to 621st lines.
Therefore, when conventional video data compliant with the analog video standards is subjected to digital format conversion, in the case of the digital 525P standard, image data for the 39th to 42nd lines and the final line, i.e., 5 lines in total, do not exist in the odd-numbered fields, and image data for the 40th to 42nd lines, i.e., 3 lines in total, do not exist in the even-numbered fields. As a result, in the period where these image data do not exist, black data is output as in other blanking periods (video blank periods). This is the same to the digital 625P standard, wherein the odd-numbered fields are identical, but the 621st line of the even-numbered field lacks data. Therefore, black data is output although it is a picture display period.
Thus, in the conventional techniques, the digital output compliant with the digital video standards cannot be produced.